Maybe Harry has an encounter with a hurt Kneazle. He decides to take it in and nurse it back to health. Through this process, he realizes how much he enjoys taking care of animals. He then begins to visit Hagrid more often to learn about different magical creatures and soon becomes known among his friends as a real pet fanatic.
He could have a Hippogriff. After Buckbeak's incident, he might develop a special bond with Hippogriffs and get one as a pet. He would need to learn how to take care of it, like making sure it has enough space to fly and proper food.
The story would likely take a very dark turn. Harry would lose a lot of his freedom. He might be locked up when Voldemort doesn't need him around.
Their relationship could start off rocky. Snape might be cold and distant at first, seeing Harry as just another responsibility. But as he gets to know Harry in his pet form, he might start to notice Harry's unique qualities and grow fond of him. For example, Harry could show loyalty and courage even in his pet state, which would gradually change Snape's view.
Maybe a mutual friend, like Hermione, could set up a situation where they have to work together on a project. As they work side by side, they start to understand each other better. Harry might realize that Draco isn't all bad, and Draco could see Harry's kindness and courage in a new light.
The story could start with Harry somehow being transported to the Star Wars universe. He'd quickly realize the power of the Force and seek out the Jedi for training. His natural magical talent would make him a fast learner. As he progresses, he could use his Hogwarts spells in creative ways against the Sith. His Gryffindor courage would be an asset in Jedi battles.
It could develop with Harry having to choose between the two worlds he now belongs to. He might start using Lucifer's power to solve problems in the wizarding world, but that would lead to unforeseen consequences. For instance, if he uses dark magic to defeat Voldemort, the wizarding world might not accept him as a hero. And as he gets more involved with Lucifer, he could lose touch with his friends and the values he held dear at Hogwarts.
The story could develop with Harry having to hide his new form from most of the wizarding world. Only a few close friends might know. He'd have to learn to control his new lich powers, which could be very dangerous if not properly harnessed.
The story could develop with a lot of drama. Harry and Narcissa would need to decide whether to keep the pregnancy a secret or make it public. If they keep it secret, there would be a constant fear of discovery. If they make it public, they would face a lot of criticism. Also, they would need to think about the upbringing of the child. Harry's friends might be shocked and some might even turn their backs on him.
The story could start with Harry noticing some strange and menacing behavior around him that he can't quite explain. As he digs deeper, he discovers it's the Joker. Harry might then try to enlist the help of his friends like Ron and Hermione. They could come up with plans to trap the Joker or at least find out what he wants. Meanwhile, the Joker would be constantly one step ahead, leaving behind his signature chaotic clues.
If Harry Potter is sealed in Naruto fanfiction, the story might start with Harry being confused and disoriented in this new world. He'd soon discover that his magic works differently here. As he tries to find a way back home, he could get involved in the conflicts between the ninja villages. His magic could be a game - changer in some of the battles, and he could become a key figure in the power struggle, either as a feared opponent or a valuable ally depending on which side he chooses.